I see your point (two unusual things being similar looks more suspicious than two common things being similar) but I think two "I–V–vi–IV" songs that were as me

I see your point (two unusual things being similar looks more suspicious than two common things being similar) but I think two "I–V–vi–IV" songs that were as melodically similar as Creep and Get Free would still be pretty suspicious. Edit: Btw I'm not sure I-III-IV-iv is that uncommon. It's in eg. David Bowie's Space Oddity and Pink Floyd's Nobody Home. It sounds to me like an old jazz / ragtime type progression although I'm struggling to come up with examples.